1. Field of the Invention
The present invention is situated in the field of materials handling technology and is generally related to a method and a device for changing the hold of flat articles being conveyed held in a gripped manner and, more particularly, for changing the hold of printed products being conveyed one after the other in an continuous stream, wherein every flat object or printed product is held by a gripper in an edge zone.
2. Description of the Related Art
Changing the hold is to be understood as a process in which every one or a predetermined selection of articles each being conveyed in a held manner by a first gripper is taken over by a second gripper, wherein the first gripper grips the article in a first edge zone and the second gripper grips the article in a second edge zone different from the first one.
A device for changing the hold of printed products conveyed in a held manner is known, for example, from the publication EP-0305671 (or U.S. Pat. No. 4,893,805). This device comprises a feeding-in device and a conveying-away device, both of which comprise a traction organ and grippers arranged thereon. The feeding-in device supplies the printed products in a substantially freely suspended manner, i.e., gripped in an upper edge zone. Upstream of the changing station, the lower parts of the freely suspended printed products are guided onto a supporting surface and in this manner are retarded relative to the gripped edges. This means that the products are brought into an inclined position such that their lower edges trail behind the gripped upper edges. The products reach the changing station in such an inclined orientation. In the area of the changing station, the grippers of the conveying-away device move along a track below the conveying track of the feeding-in device and aligned to it. The movements of the grippers of the feeding-in device and of conveying-away device are parallel and synchronized such that, at the changing station, every gripper of the conveying-away device meets with a lower edge zone of a printed product being fed-in and is capable of grasping the printed product lower edge zone. Actuation of the grippers of the two conveying devices is synchronized such that the conveying-away gripper is closed before the feeding-in gripper is opened. Accordingly, there is no moment in which the product is not gripped. The feeding-in gripper is opened as rapidly as possible after the closing of the conveying-away gripper.
Devices in accordance with the mentioned publication have the advantage that conveyance of the printed products through the changing station is continuous and always guided in a precisely defined manner and that, nonetheless, the printed products are never strained or tensioned between the two grippers. The device therefore provides a very high conveyance security and is therefore applicable for highly sensitive printed products. These advantages, however, are achieved only if the feeding-in and conveying-away and the gripper actuation are exceedingly accurately synchronized. Furthermore, the changing process is limited to a change from a hold on one edge to a hold on the opposite edge or from a hold of one zone to another zone of the same edge, and the device is dependent on the format of the products. Furthermore, the change demands a fairly long, substantially parallel conveyance of the feeding-in and conveying-away grippers. This is particularly true if the conveying-away grippers have to catch up with the trailing edges of the products in order to position these edges in the gripper mouths.
For changing the hold on a first edge of a printed product to a hold on a second edge perpendicular to the first edge according to prior art, a conveying stream of gripped printed products is transformed into an imbricated stream, in which the products are lying loosely on a conveying surface. The imbricated stream is turned around by 90xc2x0, or the individual products are turned around by 90xc2x0, and the products are thereupon gripped again by conveying-away grippers. Because product guidance in an imbricated stream is less accurate than in a gripped stream, the security and the precision of such a method is significantly lower than in the case of a direct hold changing operation. A device in which an imbricated stream is turned around is disclosed, for example, in the publication CH-617408 (or U.S. Pat. No. 4,201,377).
It is an object of the invention to create a method and a device for changing the hold of flat articles being conveyed in a held manner. It is a further object of the inventive method and device, on the one hand, to be simpler than corresponding methods and devices according to prior art and, nonetheless, not to be subject to their limitations. Therefore, using the method and device according to the invention it is possible to feed-in the flat articles held gripped in a first edge zone and to convey them away held gripped in a second edge zone, the two edges being oriented at right angles or at an oblique angle to one another. The method and the device according to the invention provides a security and holding accuracy satisfying very high demands, even in the case of very high conveying capacities.
In accordance with the method according to the invention, flat articles are held by feeding-in grippers in a leading edge zone and are pulled one after the other onto a changing support. The flat articles are positioned one after the other on the changing support by opening each gripper, and each article deposited on the changing support is pushed off the support by an open conveying-away gripper before the next article is deposited. The conveying-away gripper acts on a trailing edge zone different from the edge zone being acted on by the feeding-in gripper. During the pushing action, the conveying away gripper is closed while the article is still being held in a stable position by the changing support. The pushing movement and the conveying-away take place in one direction (conveying-away direction), which intersects with the feeding-in direction in the area of the changing station.
The pushing action can be effected as mentioned above by the conveying-away grippers. It can also be effected by other suitable pushing means, such as, for example, pusher cams. Independent of the pushing means, the articles are grasped by the conveying-away grippers while being pushed. However, if pushing means different from the conveying-away grippes are used, it becomes possible to grasp the articles in an edge zone different from the edge zone being acted on by the pushing means.
Before the conveying-away gripper is closed, the articles, if so required, can be subjected to lateral alignment.
For a high conveying capacity and relatively low conveying speed, it is advantageous to overlap the articles with one another both during the feeding-in as well as during the conveying-away. In this case, the articles are arranged in the feeding-in stream such that their gripped, leading edges are on top of the stream. In the conveying-away stream the leading edges are on top of the stream also, however, the leading edges are not the gripped edges.
The projections of the feeding-in direction and of the conveying-away direction on the surface of the changing support intersect at an angle. The intersecting angle advantageously corresponds to the angle between the edges held on feeding-in and the edges held on conveying-away. This means that, for rectangular articles being fed-in gripped at a longer edge and being conveyed away gripped at a shorter edge, the angle between the two conveying directions advantageously amounts to 90xc2x0.
It becomes manifest, in particular when utilising the invention for conveying printed products, that also in the case of very high conveying capacities and very dense conveying streams (i.e., for distances between products of approximately 10 cm at edge lengths of up to approximately 60 cm and for conveying speeds of up to approximately 1 to 2 m/sec) it is possible, to carry out the hold changing process in accordance with the invention with an adequate security and accuracy. As such, the demands of the synchronisation accuracy between feeding-in and conveying-away are significantly lower than is the case with known systems for hold changing. Furthermore, the dependence of the device on article format is significantly lower than has been the case up until now. As long as the edge zone held gripped during feeding-in and the edge zone acted on during pushing (i.e., for rectangular or square-shaped products one product corner) are aligned to a reference position, the device does not have to be modified or readjusted for handling products of differing formats.
The device according to the invention comprises a feeding-in device with feeding-in grippers, a conveying-away device with conveying-away grippers, and a changing support. The conveying-away device may further comprise separate pushing means. The changing support is arranged horizontally or inclined. The two conveying devices are arranged such that their grippers are driven from opposite sides, for example, one set of them from above, the other set from below. For the pushing function, the conveying-away grippers or the pushing means, respectively, move advantageously substantially in the plane of the surface of the changing support and are driven from below. For this purpose, the changing support comprises at least two independent parallel parts, between which the grippers move driven from below. It is also possible to provide gripper pairs driven from below, of which one gripper respectively moves on each side of the changing support, which, in this case, is narrower than the handled articles.
If the articles overlap one another in the feeding-in stream and in the conveying-away stream, the feeding-in grippers being driven from above move above the changing support and at a distance from it. If the articles do not overlap, the feeding-in grippers may move in the same plane as the conveying-away grippers and the grippers of the two kinds traverse each other""s paths in a comb-like manner.
The two conveying devices comprise, for example, conveying organs on which the grippers are arranged at equal distances, or they comprise rail tracks along which conveying elements with one gripper each are conveyed in a more or less independent manner. For synchronizing grippers arranged on conveying elements being independent of one another, the conveying elements need to be brought into phase for the hold changing process.
For opening and closing the grippers in the zone of the changing support, actuating cams are provided and the grippers comprise corresponding control rollers rolling along the cams. If not all the fed-in articles are to be subjected to the hold changing operation, the grippers will be selectively controlled.
The feeding-in device advantageously further comprises a means for braking the fed-in articles after being released from the feeding-in grippers. Such braking means keep the articles from overshooting the changing support due to their own momentum.
In the zone of the changing support there are advantageously aligning means being aligned in the direction of the conveying-away. These aligning means serve for laterally aligning the articles deposited on the changing support while being released by the feeding-in gripper and/or while being pushed across the changing support by the conveying-away grippers or the pushing means.